Shielded housing for electronic circuit or components

ABSTRACT

A shielded housing for accommodating electronic circuits or components which are sensitive to electromagnetic interference fields or radiate interference fields, is fitted with an electrical connection in the form of a connecting cable, connecting plug or the like. This housing includes a shielding in the form of a closed metallic coating (of a conductive material) and, moreover, includes filter devices which are active against interference fields in particular in the area where the connection enters or penetrates the housing. In accordance with this invention, at least in the area of entry or lead-in, filter devices with capacitors are provided which are embodied as integral components of the connecting elements and of the shielding and, possibly, of the housing walls, also.

TECHNICAL FIELD

This invention generally relates to electromagnetic shielding and moreparticularly relates to a shielded housing for accommodating electroniccircuits and/or components which are sensitive to electromagneticinterference fields and/or radiate interference fields.

BACKGROUND OF THE INVENTION

Usually electronic circuits, sensitive to irradiated high-frequencyelectromagnetic fields, are accommodated in shielded housings. Theshield protects the circuitry against the direct incidence of thehigh-frequency fields. The electric fields, however, may also reach thecircuitry indirectly via electric cables, leading into the housing, andcause electrical interference with the circuitry. Therefore, filterdevices which are active against high frequencies are provided at thepoint where the cable enters the housing. These filter devices areusually discrete feed-through filters or feed-through capacitors,respectively.

The above-described arrangement may also be used with circuits, emittinghigh-frequency electromagnetic fields, so as to protect the environmentagainst the emission of fields.

Such shielded housings usually are made from metal and the feed-throughcapacitors are soldered, screwed or pressed in. A noise-suppressing plugis described in U.S. Pat. No. 5,167,539. The walls of the plugreceptacle are of metal.

For various reasons (such as cost, weight, elasticity) often plastichousings are used. So as to achieve the desired shielding effect thesehousings are metallized. The electric connection between feed-throughcapacitor and metallization often cannot be achieved by simple means.

It is thus an object of this invention to develop a housing of the typereferred to at the beginning which is characterized by a simple design,low manufacturing expense and by a high filtering effect, in particularin the area of entry of the cables leading into the housing.

The present invention fulfills the objects of the invention in the areaof entry or lead-in, filter devices with capacitors are provided whichare embodied as integral components of the connecting elements and ofthe shield.

This invention renders the use of discrete and constructionallyexpensive feed-through capacitors superfluous. Instead, the structuresin the area of the points of penetration which consist of theelectrically conductive connections leading into the housing (such asplug pins and punched grids, injection-moulded into the housing, andother inserts), of the insulating layers (dielectrics) and of the shieldserve as feed-through capacitors.

The dielectric may be applied to the conductive connection either out ofthe housing material during the manufacture of the housing (e.g.,plastic injection-moulding processes) or by means of a further operationsuch as by lacquering, laminating, imprinting, etc.

The second capacitor plate is applied in one operation with theshielding, e.g., by means of electroplating, sputtering or lacquering.

The capacity of the feed-through capacitor constructed in accordancewith this invention may be calculated as follows:

Two-plate capacitor:

C=∈·A/s;

∈=∈₀·∈_(r), ∈₀=8.85·10⁻¹² F/m

Cylinder capacitor:

C=2π·∈·1/ln(r ₂ /r ₁)

The impedance can be calculated as follows:

X _(c)=1/(2π·f·C)

The lower the frequency to be filtered, the greater the requiredcapacity of the feed-through capacitor. A great capacity of thefeed-through capacitor is achieved by means of large surfaces A and asmall distance s of the capacitor plates.

The following advantages are achieved, with the following disadvantageseliminated:

elimination of the discrete feed-through capacitors and of all theproduction steps for their assembly;

the feed-through capacitors are manufactured without any additionaloperation, e.g., in but one cost-saving cycle of operation.

In the following, special examples of embodiments of this invention andtheir modes of operation will be described:

Two-plate capacitor:

C=∈·A/s;

∈_(r)=4.2; A=2.5 mm·7.5 mm; s=10 μm (lacquered)

C=70 pF

X_(c)=1/(2π·1.8 GHz·70 pF)=1.3 Ω

X_(c)=1/(2π·26 MHz·70 pF)=87 Ω

∈_(r)=4.2; A=2.5 mm·7.5 mm;

s=0.3 mm (plastic, injection-moulded)

C=2.3 pF

X_(c)=1/(2π·1.8 GHz·2.3 pF)=38Ω

Cylinder capacitor:

C=2π·∈·1/1n(r ₂ /r ₁); 1=3 mm

∈_(r)=4.2; r₁=0.5 mm; r₂=0.501 mm

C=350 pF

X_(c)=1/(2π·1.8 GHz·350 pF)=250 mΩ

X_(c)=1/(2π·1.8 GHz·350 pF)=17.5 Ω

The following variants of this invention are conceivable:

a combination of this invention with technologies already applied forrepresenting conductor structures on plastic housings;

a special moulding of the capacitor plates for the manufacture of filterstructures (e.g., T or pi filters) by using, e.g., the strip linetechnology.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying FIG. 1 is the perspective, schematically simplified andpartial representation of one embodiment of the present invention. Thehousing 1,2 is a section cut open so as to illustrate the embodiment ofthe point of penetration which also serves as capacitors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The housing of this representation consists of a hollow body 1, shapedlike a rectangular prism, for accommodating a (non-illustrated)electronic circuit, of a sensor or the like which is sensitive tospurious radiation, and is closed by a lid 2 represented but in part.Hollow body 1 and lid 2 comprise an enclosure.

By way of a lead-in 3 and a (non-illustrated) multi-conductor connectioncable, the housing, i.e., the electronics inside the housing, isconnected with the related external circuitry, power supply etc.

Referring to the represented example of an embodiment, a plug receptacle4 is arranged in the area of the lead-in 3 symbolized by an edgerepresented by a broken line. Strictly speaking, the lead-in 3 of thisembodiment is expanded to be a receptacle 4 accommodating the(non-illustrated) plug of a connecting cable. Three elements 4′ (i.e.points of penetration) for accommodating the plug contact are outlinedinside the receptacle 4. The elements 4′ may be designed to accommodateplug pins, punched grids, lugs, or other inserts injection-moulded intothe housing.

Housing 1, 2 of the present example of an embodiment of this inventionconsists of plastic which, on the inside of the housing, is providedwith an electrically internal conductive layer 8 serving as shielding.

What is essential in terms of invention is the embodiment of the lead-in3 or rather of the area of entry or penetration (4′) of the electricalconnection. This connection is a three-conductor connection. Theindividual connecting elements (not shown), are fed through the elements4′ of the housing 1, 2, which are connected to three pins or plates 5,5′, 6. Hereinafter, elements 5, 5′, and 6 are referred to as connectingpins 5, 5′, 6. The connecting pin 6 in the middle serves to connect theground GND, the two outer connector pins 5, 5′, serve to connect thesignal feed and the power supply, respectively.

Provided on the connector pins 5, 5′ is a layer serving as dielectric 7and, in this case, consisting of the material of the housing 1, 2. Thisdielectric 7 carries a capacitor plate layer 8′ of an electricallyconductive material conductively connected with the metallization orinternal conductive layer 8 of housing 1, namely with the shield. Inaccordance with this invention, this capacitor plate layer 8′ can bemanufactured as direct integral component of the shield or internalconductive layer 8. It is evident that, in this way, capacitors orfeed-through capacitors are simulated by the structural combination ofthe connector pins 5, 5′, the dielectric 7, and the capacitor platelayer 8′. The structural simulation of a capacitor or feed-throughcapacitor can be manufactured very easily and in a cost-saving manner.No separate manufacturing steps are required for applying the dielectric7 and the capacitor plates layer 8′. This will rather take placesimultaneously with injection-moulding and coating the walls of thehousing.

After inserting the (non-represented) electronics in the internal spaceand after connecting the electronics, the inventive housing is closed bythe lid 2 which is mounted and glued in. Preferably a conductive glue 2′is used so as to realize a completely closed shielding.

What is claimed is:
 1. A shielded housing for accommodating electroniccomponents that are sensitive to electromagnetic fields or that radiateelectromagnetic fields, comprising: an enclosure, wherein the walls ofthe enclosure are made of plastic; an electrical connection connected tosaid enclosure, said electrical connection in the form of a receptaclehaving a plurality of receptacle elements to allow a point ofpenetration for a connecting cable at a lead-in portion of theenclosure; a shield in the form of a coating applied to the inner wallsof the enclosure, said coating including a conductive material; and afilter device which is active against electromagnetic fields at thepoint of penetration area where the connecting cable enters orpenetrates the enclosure, the filter device defined as an integralcomponent of the electrical connection and of the shield.
 2. A shieldedhousing as claimed in claim 1, wherein the receptacle elements may befurther defined in a specific shape to accommodate at least one plugpin, punched grids, or lugs that may be inserted into the enclosure atthe point of penetration, wherein the receptacle and receptacle elementsare injection-moulded onto the enclosure at the lead-in portion.
 3. Ashielded housing as claimed in claim 1, wherein said capacitor platelayer of said filter device is applied in the same operation withapplying the shielding to the walls of the enclosure.
 4. A shieldedhousing as claimed in claim 3, wherein the capacitor plate layer isapplied to the shield by electroplating, sputtering, or lacquering.
 5. Ashielded housing as claimed in claim 1, wherein the filter devicefurther comprises a dielectric, connecting pins, and a capacitor platelayer.
 6. A shielded housing as claimed in claim 5, wherein the filterdevice acts as a feed-through capacitor.
 7. A shielded housing asclaimed in claim 5, wherein the dielectric is made of the same plasticmaterial as that of the enclosure.
 8. A shielded housing as claimed inclaim 7, wherein the dielectric is applied to the capacitor plate layerby plastic injection moulding, lacquering, laminating, or imprinting. 9.A shielded housing as claimed in claim 5, wherein the connecting pinsare further defined as a signal feed pin, a power supply pin, and aground pin.
 10. A shielded housing as claimed in claim 1, wherein theenclosure is further defined as having a body portion and a lid portion.11. A shielded housing as claimed in claim 10, wherein the lid portionis connected to the body portion in sealing engagement with a conductiveglue.
 12. A shielded housing for accommodating electronic componentsthat are sensitive to electromagnetic fields or that radiateelectromagnetic fields, comprising: an enclosure, wherein the walls ofthe enclosure are made of plastic; an electrical connection connected tosaid enclosure, said electrical connection in the form of a receptaclehaving a plurality of receptacle elements to allow a point ofpenetration for a connecting cable at a lead-in portion of theenclosure; a shield in the form of a coating applied to the inner wallsof the enclosure, said coating including a conductive material; and afeed-through capacitor-like filter which is active againstelectromagnetic fields at the point of penetration area where theconnecting cable enters or penetrates the enclosure, the feed-throughcapacitor-like filter defined as an integral component of the electricalconnection and of the shield.
 13. A shielded housing as claimed in claim12, wherein the receptacle elements may be further defined in a specificshape to accommodate at least one plug pin, punched grids, or lugs thatmay be inserted into the enclosure at the point of penetration, whereinthe receptacle and receptacle elements are injection-moulded onto theenclosure at the lead-in portion.
 14. A shielded housing as claimed inclaim 12, wherein the feed-through capacitor-like filter furthercomprises a dielectric, connecting pins, and a capacitor plate layer,wherein the connecting pins are further defined as a signal feed pin, apower supply pin, and a ground pin.
 15. A shielded housing as claimed inclaim 14, wherein said capacitor plate layer is applied in the sameoperation with applying the shielding to the walls of the enclosure. 16.A shielded housing as claimed in claim 15, wherein the capacitor platelayer is applied to the shield by electroplating, sputtering, orlacquering.
 17. A shielded housing as claimed in claim 14, wherein thedielectric is made of the same plastic material as that of theenclosure.
 18. A shielded housing as claimed in claim 17, wherein thedielectric is applied to the capacitor plate layer by plastic injectionmoulding, lacquering, laminating, or imprinting.
 19. A shielded housingas claimed in claim 12, wherein the enclosure is further defined ashaving a body portion and a lid portion, wherein the lid portion isconnected to the body portion in sealing engagement with a conductiveglue.
 20. A shielded housing for accommodating electronic componentsthat are sensitive to electromagnetic fields or that radiateelectromagnetic fields, comprising: an enclosure, wherein the walls ofthe enclosure are made of plastic, wherein the enclosure is furtherdefined as having a body portion and a lid portion, wherein the lidportion is connected to the body portion in sealing engagement with aconductive glue; an electrical connection connected to said enclosure,said electrical connection in the form of a receptacle having aplurality of receptacle elements to allow a point of penetration definedas a three-conductor connection for a connecting cable at a lead-inportion of the enclosure, wherein the receptacle elements may be furtherdefined in a specific shape to accommodate at least one plug pin,punched grids, or lugs that may be inserted into the enclosure at thepoint of penetration, wherein the receptacle and receptacle elements areinjection-moulded onto the enclosure at the lead-in portion; a shield inthe form of a coating applied to the inner walls of the enclosure, saidcoating including a conductive material; and a feed-throughcapacitor-like filter which is active against electromagnetic fields atthe point of penetration area where the connecting cable enters orpenetrates the enclosure, the feed-through capacitor-like filter definedas an integral component of the electrical connection and of the shield,wherein the feed-through capacitor-like filter further comprises:connecting pins for the three-conductor connection, wherein theconnecting pins are further defined as a signal feed pin, a power supplypin, and a ground pin, a capacitor plate layer, wherein said capacitorplate layer is applied in the same operation with applying the shieldingto the walls of the enclosure, wherein the capacitor plate layer isapplied to the shield by electroplating, sputtering, or lacquering, anda dielectric, wherein the dielectric is made of the same plasticmaterial as that of the enclosure, wherein the dielectric is applied tothe capacitor plate layer by plastic injection moulding, lacquering,laminating, or imprinting.